Method of manufacturing a superconducting oxide pattern by laser sublimation

ABSTRACT

A superconducting ceramic film is deposited on a substrate by sputtering. In virtue of the low thermal conductivity of ceramic, a laser beam is irradiated to the ceramic film in order to remove the irradiated portion by sublimation and produce a pattern on the ceramic film.

This is a divisional application or Ser. No. 07,538,740 filed Jun. 15,1990, which is divisional application of Ser. No. 07/174,503, filed Mar.28, 1988 now U.S. Pat. No. 4,957,900.

BACKGROUND OF THE INVENTION

This invention relates to a method of maufacturing a superconductingpattern by light irradiation.

There have been known the use of matallic materials such as Nb₃ Ge, withwhich it is possible to wind a coil to form a superconducting magnethaving a high Tc since a metallic material has a high ductility andmalleability. On the other hand, such a metallic material requires theuse of liquid helium when operated in superconduction. In recent years,superconducting ceramics are attracting interest of researchers whichhave a high Tc.

However, such superconducting ceramics are fragile because of lowductility and malleability so that it is entirely impossible to form asuperconducting coil with a wire made of such superconducting ceramics.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a high Tcsuperconductor in the form of wire or strip.

It is therefore an object of the invention to provide a method ofmanufacturing a high Tc superconductor in the form of wire or stripwhich is suitable for mass-production.

In accordance with one aspect of the present invention, an oxide (orcarbonate) mixture for constituting a superconducting ceramic is firstformed in the form of a thin film on a substrate by sputtering, printingsuch as screen press printing or other methods. When deposited bysputtering, the structure of the ceramic material of the film becomesamorphous or another structure which are abundant in lattice defect orimferfection so that the resistivity of the ceramic material is usuallyrather high. The deposited ceramic can be transformed into a desiredsuperconducting ceramic by thermal oxidation or firing.

The inventor has found that such a ceramic type superconducting film canbe easily processed by laser scribing accompanied by sublimation sinceits thermal conductivity is relatively small. The ceramic film can beprocessed by laser irradiation before or after firing. For example, astrip of the ceramic material can be removed or remains on a substrate.In this invention, any laser can be employed which is suitable for thecase, such as a YAG laser (1.06 micron in wavelength), an excimer laser(KrF, KrCl and so forth), a CO₂ laser or an N₂ laser. A YAG laser canemit a laser beam having a circular cross section repeatedly at 5 to 100KHz. When an excimer laser is used, a shaped beam having a cross sectionof a circle (10-100 microns in diameter) or a linear cross section(10-40 cm wide 5-100 microns long) can be obtained by (expanding and)squeezing with an optical system.

BRIEF DESCRIPTION OF THE INVENTION

FIG. 1 is a perspective view showing a manufacturing process ofsuperconducting ceramic pattern in accordance with the presentinvention.

FIG. 2 is a perspective view showing another embodiment of themanufacturing process of superconducting ceramics in accordance with thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a manufacturing process in accordance with thepresent invention will be described. In FIG. 1(A), a substrate 1 is madeof a ceramic material such as alumina, silicon oxide, silicon nitride,alminium nitride, strontium titanate, zirconia, yttria or YSZ(yttriastabilized zircon), or a metal such as copper or a copper alloy orglass. YSZ, yttria or zirconia are particularly suitable for this casefrom the view point of the coefficient of thermal expansion rate. Anywaythe material should be selected so that the differential coefficient ofthermal expansion between the underlying substrate and the ceramic thinfilm to cover them should be limited preferably within 50% of theceramic thin film. If the coefficients of the substrate and the ceramicthin film are substantially different, strain may hinder the ceramicfilm from being recrystallized into superconducting structure by thermalannealing. On the substrate 1 is formed a ceramic film 2 conforming toYBa₂ C₃ O₆₋₈ with 0.1 to 50 micron in thickness, e.g. 20 microns bysputtering or printing method such as screen press printing.

The ceramic film 2 is fired at 500°-1000° C., e.g. 900° C. for 15 hoursand transformed to a superconducting structure. A laser beam having awavelength of 1.06 microns from a YAG laser is radiated to thesuperconducting film 2 to produce a pattern thereon. The surface of thefilm is scanned to the right direction from the left edge as shown inFIG. 1 so that a portion of the film is removed by sublimation leaving agroove 3. The appropriate output power is 10⁶ to 10⁷ W/sec. Strongerirradiation may damage the underlying substrate 1. Alternatively, thelaser patterning can be effected before the firing step which tranformsthe ceramic film into a superconducting structure in which oxygen andcopper atoms form a layer-structure.

An excimer laser instead of the YAG laser may be used which is capableof emitting a series of intense laser pulses with a rectangular crosssection of 20×30 mm² for example. The pulse is shaped into a linearcross section 10 cm wide and 50 microns thick. Each circular pulse isradiated to an irradiating region prescribed on the film which shares a60-80% area with the irradiating region for the preceding pulse (andalso of the subsequent pulse). The scanning speed is 2 m/min. Thefrequency is 5-30 KHz, e.g. 10 KHz. By virtue of this irradiation, theirradiated portions of the ceramic film are selectively removed bysublimation. The entire substrate may be heated during the laserprocessing to 300°-800° C., e.g. 600° C. by a halogen lamp.

FIG. 2 shows second embodiment of the invention. In this embodient,substantially same procedure is repeated as the preceding embodimentexcept described below.

The substrate 1 is a cylinder. On the substrate is deposited a ceramicfilm 2 while the substrate 1 is rotating in the direction indicated byan arrow 12. After drying the film, a laser beam having a 50 micronsdiameter is radiated repeatedly to the substrate. The position of thelaser beam is shifted to the right direction (the axial direction of thecylinder 1) while the substrate 1 is rotating around its axis. By thisprocess, a continuous helical supercondutor 5 is formed on thecylinder 1. Each part of the helix 5-1 is isolated from the adjacentpart 5-2 by the helical groove 3 which has been removed by lasersublimation. As a result, a superconducting electromagnet in the form ofa coil is constructed.

When laser annealing is utilized in addition to laser sublimation, anadvanced process can be performed. First, a ceramic film is formed on asurface in such a way that the film does not have yet superconductingstructure. A prescribed portion of the film is melted by irradiationwith a laser beam (laser annealing). The irradiated portion is endowedwith superconducting property by recrystallization during cooling. Inthe same time, the ceramic film may be cooled if necessary. Then,another prescribed portion of the ceramic film is removed by lasersublimation. By this process, ceramic pattern which may be composed ofsuperconducting regions and non-superconducting (insulating) regions canbe obtained. Whether a laser irradiation is effected as sublimation orannealing is depending on the laser emission condition (laser power orintensity).

Superconducting ceramics for use in accordance with the presentinvention also may be prepared in consistence with the stoichiometricformulae (A_(1-x) B_(x))_(y) Cu_(z) O₂, where A is one or more elementsof Group IIIa of the Priodic Table, e.g., the rare earth elements, B isone or more elements of Group IIa of the Periodic Table, e.g., thealkaline earth metals including beryllium and magnesium, and x=0-1;y=2.0-4.0, preferably 2.5-3.5; z=1.0-4.0, preferably 1.5-3.5; andw=4.0-10.0, preferably 6.0-8.0. One example is YBa₂ Cu₃ O₆₋₈. Also,superconducting ceramics for use in accordance with the presentinvention may be prepared consistent with the stoichiometric formulae(A_(1-x) B_(x))_(y) Cu_(z) O₂, where A is one or more elements of GroupVb of the Priodic Table such as Bi, Sb and As, B is one or more elementsof Group IIa of the Periodic Table, e.g., the alkaline earth metalsincluding beryllium and magnesium, and x=0.3-1; y=2.0-4.0, preferably2.5-3.5; z=1.0-4.0, preferably 1.5-3.5; and w=4.0-10.0, preferably6.0-8.0. Examples of this general formula are BiSrCaCuCu₂ O_(x) and Bi₄Sr₃ Ca₃ Cu₄ O_(x). Tc onset and Tco samples confirmed consistent withthe formula Bi₄ Sr_(y) Ca₃ Cu₄ O_(x) (y is around 1.5) were measured tobe 40°-60° K., which is not so high. Relatively high criticaltemperatuers were obtained with samples conforming to the stoichiometricformulae Bi₄ Sr₄ Ca₂ Cu₄ O_(x) and Bi₂ Sr₃ Ca₂ Cu₂ O_(x). The numberdesignating the oxygen proportion is 6-10, e.g. around 8.1.

While a description has been made for several embodiments, the presentinvention should be limited only by the appended claims and should notbe limited by the particular examples.

I claim:
 1. A method of making a high-temperature superconductor deviceby laser scribing comprising the steps of:forming a superconductingceramic layer on a surface; directing pulses of a laser beam into a zoneof the superconducting ceramic layer to remove a portion thereof bylaser sublimation.
 2. A method as claimed in claim 1 wherein said laseris an excimer laser.
 3. A method as claimed in claim 2 wherein saidexcimer laser is a KrF or KrCl excimer laser.
 4. A method ofmanufacturing a superconducting ceramic pattern comprising:forming asuperconducting ceramic layer on a surface and irradiating and subliminga portion of said ceramic layer with a sequence of pulses of a laserbeam to remove the irradiated portion of said ceramic layer.
 5. Themethod of claim 4 wherein said superconducting ceramic layer isdeposited on said surface by sputtering.
 6. The method of claim 4wherein said pulses are irradiated to a portion of said ceramic layertracing a line thereon.
 7. The method of claim 4 wherein said surface isthe periphery of a cylinder and said laser beam is irradiated to a helixon said periphery to form a superconducting coil.
 8. The method of claim7 wherein said cylinder is turning around its axis during saidirradiating step while the irradiation position of said laser beam isonly shifted in the axial direction with respect t o said cylinder.